Polyurethane polymers generally contain carbamate groups, (—NHCOO—), also referred to herein as urethane groups, and urea groups (CO(NH)2) in their backbone structure. They are typically formed by the reaction of a diisocyanate with a polyol and polyamines. In the last several years, aqueous based-polyurethane dispersions are becoming increasingly used in a variety of applications such as, but not limited to, ink, surface coatings such as roof, floor, flexible, plastic, and specialty coatings, and adhesives. The prior art provides many examples of aqueous-based polyurethane dispersions and methods for making same such as, but not limited to, U.S. Pat. Nos. 4,528,323; 4,871,798; 5,124,400; 5,270,433; 5,432,228; 5,494,960; 5,576,382; 5,616,400; 5,703,158; 5,981,650; and 6,433,073.
Polyurethane adhesives are known for excellent adhesion, flexibility, toughness, high cohesive strength, and fast cure rates. In certain applications, polyurethane adhesives rely on the curing of multifunctional isocyanate-terminated prepolymers with moisture or on the reaction of the adhesive with the substrate, e.g., wood and cellulosic fibers. Two-component adhesives consist of an isocyanate prepolymer, which is cured with low equivalent weight diols, polyols, diamines, or polyamines. Such systems can be used neat or as solution. The two components are kept separately before application. Two-component polyurethane systems are also used as hot-melt adhesives. Water-borne adhesives are preferred because of restrictions on the use of solvents. In this connection, low viscosity prepolymers are emulsified in water, followed by chain extension with water-soluble glycols or diamines.
Adhesives are being increasingly used in the manufacture of electronic devices. In such devices, the application of the adhesive, specific bonding process and electrical properties of the material are increasingly becoming critical to the overall performance and lifetime of the electronic device. The adhesive typically should perform similarly at one condition after being exposed to different conditions. For example, a device that shows good contrast ratio and switching times at 25° C. and 80% relative humidity, should have the same performance when returned to this condition after being exposed to high or low temperatures and humidity for short periods of time. This requirement necessitates that the adhesive electrical properties and adhesion are not altered by exposure to these conditions. It is believed that the electrical properties of the adhesive, specifically volume resistivity and/or conductivity, are related to the materials ability to be ionically conductive.
There are many patents and descriptions of such adhesive materials that are used in electronic devices that demonstrate certain adhesive and electrical properties. However, most of these materials refer to curable systems that are filled with conductive media. Relatively fewer references to non-curable adhesives are provided. This is especially true of lamination adhesives made using aqueous polyurethane dispersions having a polyurethane polymer contained therein that have the potential to serve as ionically conducting polymeric electrolytes.
All references cited herein are incorporated herein by reference in their entirety.